Designed for shipping fish and corals, used by wholesaler and exportes worldwide. These 30 hour heat packs will activate in 30 minutes and will peak at a surface temperature of 115 degrees in 14 hours. One heat pack will increase the temperature of a 1cu. ft. box by 15 degrees, each additional heat pack will increase it another 10 degrees. Use enough heat packs to keep the box at 60-70 degrees, the goal is to keep the box from freezing, not to maintain tank temperatures. For example, in a box being shipped in 40F should have two heat packs. It is best to wrap the heat pack in newspaper, air is needed to activate the heat pack. If the temperature of the box drops below 32F, the water in the heatpack will freeze and the heat pack will no longer work.